This invention relates to deadband adjustment and more particularly to pressure switches with deadband adjustment.
A snap action device employing a belleville spring with adjustments operable to increase or decrease the resistance of the belleville spring to provide a snap action response at a predetermined force is known from U.S. Pat. No. 3,030,096.
In prior U.S. Pat. No. 3,876,845, in which I am a co-inventor, there is described the theoretical analysis of certain spring rate and load considerations. The deadband is defined as the difference between actuating and reset pressures, i.e., increasing and decreasing pressure settings.
As is known from the prior art, pressure switches require adjustability of the difference between operating pressure and reset pressure (deadband). A number of the known devices incorporate adjustment of the electrical switch operating characteristics, the pressure sensor movement, or by introduction of a step change in spring rate somewhere within the operating movement. The later only working with positive rate devices. However, all prior art devices do not adequately function in combination with snap action devices, such as the belleville spring devices referenced above. Further, most prior art adjustments can lead to failure of the pressure switch due to the switch element being adjustable to a zero contact gap or the sensor motion being adjustable to zero.
Accordingly, the problem of deadband adjustment of pressure switches is solved by the invention.